If you enjoy the flavor of, say, Norse mythology, you might like Kalevala a lot. It's an epic poem so finding a good translation is important. Lord of the Rings is not based on Kalevala but some of the Silmarillion is.
OK, so that's where I had heard the connection previously. Sounds like "The Children of Hurin" is an expansion of the tale mentioned in "The Silmarillion", so that's where the connection to the "Kalevala" must be.
I'm half Finnish, but have not read much of the Kalevala. I believe that Longfellow used the rhythm pattern of this poem for his 'Tales of Hiawatha' epic, which is a good way for non-Finns to get the feel of speaking Finnish.
This accidental incest plot of course goes back to the Greek myth of Oedipus Rex, who kills his father and marries his mother, all unknowingly, and in Wagner's Ring Sigemund commits accidental incest with Siegelinde, not knowing she is his sister. The Ring was based in part of the ancient tales of the Niebelungen, which itself is based on the history of the Germanic tribes at the time of the invasion by Attila the Hun. (since the Finns, like the Hungarian Magyars, are related to the Huns, this rather comes full circle.)
These themes are some of the most ancient and powerful themes in human culture. If you get to dwelling on them too much, you must move to the land of the Sun -- Florida.